Wooden panels are commonly used as sheathing material in North American residential construction. In these applications the wooden panels are attached to framing members (usually wood-based) by use of metallic fasteners in floors, walls and roofs. Key requirements of the panels have historically included structural and enclosure functions. In many cases the sheathing panels must also act as a “nailing base” for adjacent building materials. For instance, exterior siding is often nailed directly to exterior wall sheathing. Shingles are generally tacked to roof sheathing. Decorative hardwood flooring is stapled or otherwise connected to floor sheathing.
As global demand for energy and conservation have recently increased, code requirements for thermal insulation have been elevated. This situation has created a need for materials with greater thermal insulation to be incorporated into the framing and sheathing elements of the building envelop. Conventional wooden sheathing panels, including plywood and oriented strandboard (OSB), generally have a thermal resistance value (R value) of about 0.45-0.75 hr·ft2F/BTU, which is insufficient to meet emerging energy codes without the use of supplemental insulating materials. In contrast, closed-cell polyurethane rigid foam insulation boards that are filled with argon can have a thermal resistance per inch value of about 3.0-5.5 hr·ft2F/BTU, for 0.5″ and 1.0″ thick rigid foam, respectively.
Manufacturers of polyurethane rigid foam insulation board recommend the use of these products in wall systems either as an additional layer adjacent to wooden sheathing panels or in some cases as a replacement for the wooden sheathing panels. In many cases, use of the polyurethane rigid foam insulation board in this manner will satisfy energy code requirements. Unfortunately, the polyurethane rigid foam insulation board has structural properties that are substantially less than those of the wooden sheathing. Thus, replacing the wooden sheathing with polyurethane rigid foam insulation board generally decreases the racking strength and out-of-plane bending strength of the wall and its ability to resist wind and seismic loads. Use of the polyurethane rigid foam insulation board as a replacement for wooden wall sheathing also creates a situation in which exterior siding can no longer be nailed directly into the wall sheathing. This complication can be partially overcome if installers are sufficiently skilled to inject nails through the exterior siding, through the foam board and into the wooden studs inside of the wall, but the gap between the portion of the nail that is in the exterior siding and that which is in the wooden stud will be subjected to high shear and bending stresses that are not normally present when the exterior siding is attached directly to a structural material. Thus, builders have been resistant to utilize the polyurethane rigid foam insulation board and have expressed a need for alternative building materials that will allow them to comply with new energy codes without adversely impacting structural properties and with minimum change to traditional building practices.
Codes have also emerged regarding sound transmission in both residential and commercial construction in the United States. In general, these codes require the use of materials that limit transmission of sound across floors and walls to a given threshold.
In view of the needs of the construction industry described above, improved materials for reducing sound and thermal transmission are desirable.